Count of multiple face areas
This worked for me in Blender 2.82.  Result is shown in System Console window.

import bpy

bpy.context.object.update_from_editmode() 
#applies any pending edits.
#allows script to be run from within edit mode

the_area = 0
for poly in bpy.context.object.data.polygons:
    if poly.select:
        the_area += poly.area

print('final area total')
print(the_area)